www.德州仪器.com
−160
−140
−120
−100
−80
−60
−40
−20
0
20
0 25 50 75 100 125
振幅 − db
f − 频率 − hz
8192 点
f
s
= 250 ksps
f
i
= 1 khz, 0db
sinad = 73.47 db
thd = −94.03 db
振幅 − db
f − 频率 − hz
−160
−140
−120
−100
−80
−60
−40
−20
0
20
0 25 50 75 100 125
8192 点
f
s
= 250 ksps
f
i
= 45 khz, 0db
sinad = 73.62 db
thd = −94.03 db
BASICOPERATION
STARTINGACONVERSION
ADS8504
SLAS434–JUNE2005
typicalcharacteristics(持续)
FFT
figure15.
FFT
figure16.
Figure17showsabasiccircuittooperatetheads8504withafullparalleldataoutput.takingr/c(pin24)低
foraminimumof40ns(1.75µsmaxifbusyisusedtolatchthedata)initiatesaconversion.busy(pin26)
goeslowandstayslowuntiltheconversioniscompletedandtheoutputregistersareupdated.dataisoutputin
binary2'scomplementwiththemsbonpin6.busygoinghighcanbeusedtolatchthedata.allconvert
commandsareignoredwhilebusyislow.
theads8504beginstrackingtheinputsignalattheendoftheconversion.allowing4µsbetweenconvert
commandsassuresaccurateacquisitionofanewsignal.
theoffsetandgainareadjustedinternallytoallowexternaltrimmingwithasinglesupply.theexternalresistors
compensateforthisadjustmentandcanbeleftoutiftheoffsetandgainarecorrectedinsoftware(refertothe
calibrationsection).
thecombinationofcs(pin25)andr/c(pin24)lowforaminimumof40nsimmediatelyputsthesample/holdof
theADS8504intheholdstateandstartsconversion
n
.busy(pin26)goeslowandstayslowuntilconversion
n
iscompletedandtheinternaloutputregisterhasbeenupdated.allnewconvertcommandsduringbusyloware
ignored.csand/orr/cmustgohighbeforebusygoeshighoranewconversionisinitiatedwithoutsufficient
timetoacquireanewsignal.
theads8504beginstrackingtheinputsignalattheendoftheconversion.allowing4µsbetweenconvert
commandsassuresaccurateacquisitionofanewsignal.refertoTable1forasummaryofcs,r/c,andbusy
statesandFigure19,Figure20,和Figure21forthetimingdiagrams.
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